Polyaxial pedicle screw having a rotating locking element

ABSTRACT

A screw and coupling element assembly for use with an orthopedic rod implantation apparatus includes a screw with a head and a shaft extending from the head, a coupling element with a seat within which the head is seatable such that the shaft protrudes from the coupling element, and a locking element mateable with the coupling element and when mated is selectively movable through a plurality of positions including unlocked and locked positions. When in the unlocked position, the locking element presents a rod-receiving channel and the head is movable in the seat such that the shaft is directable in a plurality of angles relative to the coupling element. When in the locked position, a rod disposed within the rod-receiving channel is fixed relative to the coupling element and the head is immovable in the seat such that the shaft is fixed at an angle relative to the coupling element.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuing application of U.S. patentapplication Ser. No. 10/115,747 entitled “Polyaxial Pedicle Screw Havinga Rotating Locking Element”, filed Apr. 3, 2002.

FIELD OF THE INVENTION

[0002] The invention relates generally to screws and coupling elementassemblies for use with orthopedic fixation systems. More particularly,the invention relates to a screw and coupling element assembly, for usewith an orthopedic rod implantation apparatus, that includes a lockingelement that simultaneously locks a head of the screw within a seat ofthe coupling element so that a shaft of the screw is fixed at an anglerelative to the coupling element and a rod, of the orthopedic rodimplantation apparatus, disposed within a rod-receiving channel of thelocking element is fixed relative to the coupling element.

BACKGROUND OF THE INVENTION

[0003] The bones and connective tissue of an adult human spinal columnconsists of more than twenty discrete bones coupled sequentially to oneanother by a tri-joint complex which consist of an anterior disc and thetwo posterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than twenty bones are anatomically categorized as beingmembers of one of four classifications: cervical, thoracic, lumbar, orsacral. The cervical portion of the spine, which comprises the top ofthe spine, up to the base of the skull, includes the first sevenvertebrae. The intermediate twelve bones are the thoracic vertebrae, andconnect to the lower spine comprising the five lumbar vertebrae. Thebase of the spine is the sacral bones (including the coccyx). Thecomponent bones of the cervical spine are generally smaller than thoseof the thoracic and lumbar spine.

[0004] Referring now to FIGS. 1, 2, and 3, top, side, and posteriorviews of a vertebral body, a pair of adjacent vertebral bodies, and asequence of vertebral bodies are shown, respectively. The spinal cord ishoused in the central canal 10, protected from the posterior side by ashell of bone called the lamina 12. The lamina 12 includes a rearwardlyand downwardly extending portion called the spinous process 16, andlaterally extending structures which are referred to as the transverseprocesses 14. The anterior portion of the spine comprises a set ofgenerally cylindrically shaped bones which are stacked one on top of theother. These portions of the vertebrae are referred to as the vertebralbodies 20, and are each separated from the other by the intervertebraldiscs 22. The pedicles 24 comprise bone bridges which couple theanterior vertebral body 20 to the corresponding lamina 12.

[0005] The spinal column of bones is highly complex in that it includesover twenty bones coupled to one another, housing and protectingcritical elements of the nervous system having innumerable peripheralnerves and circulatory bodies in close proximity. In spite of thesecomplexities, the spine is a highly flexible structure, capable of ahigh degree of curvature and twist in nearly every direction. Genetic ordevelopmental irregularities, trauma, chronic stress, tumors, anddisease, however, can result in spinal pathologies which either limitthis range of motion, or which threaten the critical elements of thenervous system housed within the spinal column. A variety of systemshave been disclosed in the art which achieve this immobilization byimplanting artificial assemblies in or on the spinal column. Theseassemblies may be classified as anterior, posterior, or lateralimplants. As the classifications suggest, lateral and anteriorassemblies are coupled to the anterior portion of the spine, which isthe sequence of vertebral bodies. Posterior implants generally comprisepairs of rods, which are aligned along the axis which the bones are tobe disposed, and which are then attached to the spinal column by eitherhooks which couple to the lamina or attach to the transverse processes,or by screws which are inserted through the pedicles.

[0006] “Rod assemblies” generally comprise a plurality of such screwswhich are implanted through the posterior lateral surfaces of thelaminae, through the pedicles, and into their respective vertebralbodies. The screws are provided with upper portions which comprisecoupling elements, for receiving and securing an elongate rodtherethrough. The rod extends along the axis of the spine, coupling tothe plurality of screws via their coupling elements. The rigidity of therod may be utilized to align the spine in conformance with a moredesired shape.

[0007] It has been identified, however, that a considerable difficultyis associated with inserting screws along a misaligned curvature andsimultaneously exactly positioning the coupling elements such that therod receiving portions thereof are aligned so that the rod can be passedtherethrough without distorting the screws. Attempts at achieving properalignment with fixed screws is understood to require increased operatingtime, which is known to enhance many complications associated withsurgery. Often surgical efforts with such fixed axes devices cannot beachieved, thereby rendering such instrumentation attempts entirelyunsuccessful.

[0008] The art contains a variety of attempts at providinginstrumentation which permit a limited freedom with respect toangulation of the screw and the coupling element. These teachings,however, are generally complex, inadequately reliable, and lacklong-term durability. These considerable drawbacks associated with priorart systems also include difficulty in properly positioning the rod andcoupling elements, and the tedious manipulation of the many parts thatare used in the prior art to lock the rod, the screw, and the couplingelement in position once they are properly positioned. It is not unusualfor displacement to occur as these parts are manipulated to lock theelements, which is clinically unacceptable, and repeated attempts atlocking the elements in proper position must be made to remedy thisdisplacement.

[0009] There is, therefore, a need for a screw and coupling elementassembly which provides a polyaxial freedom of implantation angulationwith respect to rod reception. There is also a need for such an assemblywhich comprises a reduced number of elements, and which correspondinglyprovides for expeditious implantation. There is also a need for such anassembly that provides reduced difficulty in locking steps to preventunwanted displacement of the elements prior to locking. There is also aneed for an assembly which is reliable, durable, and provides long termfixation support.

SUMMARY OF THE INVENTION

[0010] The invention provides a screw and coupling element assembly foruse with an orthopedic rod implantation apparatus. The assembly includesa securing element such as, for example, a screw, that has a head and ashaft that extends from the head. Preferably, the head has an engagementsurface that can be engaged by a screwdriving tool. Preferably, the headalso has a curvate proximal portion from which the shaft extends.

[0011] The screw and coupling element assembly further includes acoupling element and a locking element. The coupling element has a seatwithin which the head of the screw can be seated such that the shaft ofthe screw protrudes from the coupling element. The locking element canbe mated with the coupling element and thereafter can be selectivelymoved through a plurality of positions including an unlocked positionand a locked position. When the locking element is in the unlockedposition, the locking element presents a rod-receiving channel and thehead of the screw is movable in the seat of the coupling element, suchthat the shaft of the screw can be directed in a plurality of anglesrelative to the coupling element. When the locking element is in thelocked position, a rod disposed within the rod-receiving channel isfixed relative to the coupling element, and the head of the screw isimmovable in the seat of the coupling element, such that the shaft ofthe screw is fixed at an angle relative to the coupling element. Moreparticularly, when the locking element is in the locked position, thelocking element is compression locked within the coupling element, thehead of the screw is compression locked within the seat of the couplingelement, and the rod is compression locked within the rod-receivingchannel.

[0012] Preferably, at least one feature on the locking element can beused to move the locking element through the positions when the lockingelement is disposed within the coupling element. Preferably, the featurecomprises an engagement surface that can be engaged by a correspondingsurface of a tool, such that the tool can engage the engagement surfaceof the feature and effectively move the locking element. Preferably, thecorresponding surface of the tool can engage the engagement surface ofthe feature despite the presence of the rod in the rod-receivingchannel.

[0013] Preferably, the seat of the coupling element can be defined by abore in the coupling element and a socket defined by a curvate volumeadjacent the bore. The curvate volume corresponds to the curvateproximal portion of the head of the screw such that the curvate proximalportion can be nested in the socket. When the curvate proximal portionof the head of the screw is nested in the socket, the shaft of the screwprotrudes from the bore and the curvate proximal portion cannot passfully through the bore. When the locking element is in the unlockedposition, the curvate proximal portion of the head of the screw canrotate and angulate in the socket such that the shaft of the screw canbe directed through a range of angles relative to the coupling element.When the locking element is in the locked position, the curvate proximalportion of the head of the screw is immovable in the socket such thatthe shaft of the screw is fixed at an angle relative to the couplingelement.

[0014] Preferably, the locking and unlocking action of the lockingelement is effected as follows. The head of the screw has a distalportion defined by a compression surface and the locking element has apermissive surface that is presented to the compression surface of thehead of the screw when the locking element is in the unlocked position.When presented with the permissive surface of the locking element, thecompression surface of the head of the screw is unhindered such that thehead of the screw is movable in the seat of the coupling element. Thelocking element also has a confrontational surface that is presented tothe compression surface of the head of the screw when the lockingelement is in the locked position. The confrontational surface of thelocking element is defined by a recess that has a recessed surfacecorresponding to the compression surface of the head of the screw.Therefore, when the locking element is in the locked position: (1) thelocking element is compressed within the coupling element, (2) thecompression surface of the head of the screw is compressed by theconfrontational surface of the locking element such that the curvateproximal portion of the head of the screw is compressed toward the boreof the coupling element and the head of the screw is immovable in theseat of the coupling element, and (3) the compression surface of thehead of the screw seats in the recess of the confrontational surface andthereby is biased against retreat from the recess. The compressionsurface of the head of the screw can be a curvate surface and theconfrontational surface of the locking element can extend from an edgeof the permissive surface of the locking element and terminate in therecess of the confrontational surface. The confrontational surface ofthe locking element preferably becomes increasing confrontational andtherefore is gradually presented to the compression surface of the headof the screw as the locking element is moved from the unlocked positionto the locked position.

[0015] Preferably, the rod-receiving channel, presented by the lockingelement when the locking element is in the unlocked position, is definedby substantially parallel walls. When the locking element is in thelocked position, the walls are compressed toward one another such thatthe rod is compressed within the channel and thereby fixed relative tothe coupling element. Preferably, the walls are increasingly compressedtoward one another as the locking element is moved from the unlockedposition to the locked position.

[0016] Preferably, the coupling element has a bore that permits use ofthe screwdriving tool when the head is seated in the seat, allowing thescrewdriving tool to engage the head as described above. Alsopreferably, the locking element has a bore that permits use of thescrewdriving tool when the locking element is disposed within thecoupling element in an unlocked position and the head is seated in theseat, allowing the screwdriving tool to engage the head as describedabove.

[0017] A use of the invention can be summarized as follows. First, thelocking element is disposed within the coupling element. Then, thelocking element is rotated within the coupling element until the lockingelement is in the unlocked position. The top bores of the lockingelement and the coupling element will then permit the insertion of thescrew into the seat of the coupling element. The surgeon can freelyrotate and angulate the screw in the socket to direct the shaft in theclinically appropriate direction for secure lodging in a vertebral bone.

[0018] Once the surgeon directs the shaft of the screw in the clinicallyappropriate direction, he passes the operative end of the screwdrivingtool through the top bores to engage the head of the screw to rotate thescrew and drive the shaft of the screw into the vertebral bone. Apre-drill hole is usually provided in the bone, into which it is desiredthat the screw be disposed.

[0019] Typically, the surgeon will repeat the process described aboveusing additional screws, coupling elements, and locking elements,lodging the additional screws into the same vertebral bone or othervertebral bones, depending on the clinically desirable result. To thatend, the invention encompasses an orthopedic rod implantation apparatushaving a plurality of screws and coupling elements of the typesdescribed above, and at least one elongate rod. Many implantations willrequire the use of two rods, however, only one rod or more than two rodsmay be necessary. The surgeon will, for example, lodge two screws into afirst verterbal bone (the screws are positioned laterally adjacent oneanother in the same bone, one in each pedicle), and lodge two otherscrews into a second vertebral bone (the screws are positioned laterallyadjacent one another in the same bone, one in each pedicle) that may beadjacent the first vertebral bone or may be separated from the firstvertebral bone by other vertebral bones that are damaged or unstable.

[0020] In a healthy spine, each screw in one of the pairs would roughlyalign with the corresponding screw in the other pair, because thevertebral bones would be vertically aligned. However, in some cases, thescrews will not be aligned because the spine is laterally crooked andthe surgeon is installing the implant to realign the vertebral bones.Therefore, in such cases, once the screws are in place, and theassociated coupling elements and locking elements are in the unlockedposition, presenting respective rod-receiving channels, and free torotate and angulate with respect to the head of the associated screw,the surgeon inserts a rod into one rod-receiving channel, and thereafterinto another rod-receiving channel, so that the rod lines up theverterbral bones affected thereby in a clinically desirable manner,urging them, typically, into vertical alignment. The surgeon similarlyinserts a second rod into the remaining two rod receiving channels tobalance the alignment forces.

[0021] Once the rods are in the rod receiving channels, the surgeonproceeds to move each locking element into the locked position byrotating the locking element. As the locking element is moved to thelocked position, the permissive surface, of the locking element, that ispresented to the compression surface of the head of the screw when thelocking element is in the unlocked position, is removed and thecompression surface is increasingly presented with the confrontationalsurface. This causes the curvate proximal portion of the head of thescrew to be increasingly compressed toward the bore until the head isimmovable in the seat of the coupling element. Ultimately, thecompression surface seats in the recess and thereby is biased againstretreat from the recess. This prevents accidental reverse rotationalslippage of the locking element from occurring and moving the lockingelement to the unlocked position.

[0022] In addition, as the locking element is moved to the lockedposition, the rod-receiving channel presented by the locking elementwhen the locking element is in the unlocked position gradually closes.Ultimately, the channel is completely closed. This prevents the rod fromlaterally exiting the locking element. Further, the walls of the channelare gradually compressed toward one another, until they ultimatelysecure the rod between them so that the rod is fixed relative to thecoupling element. This prevents the rod from axially exiting the lockingelement.

[0023] In addition, as the locking element is moved to the lockedposition, the locking element itself is gradually compressed within thecoupling element until it ultimately is secured within the couplingelement. More specifically, as the rod seeks to radially force the wallsand apart, the outer surface of the locking element seeks to radiallypush against the inner surface of the coupling element. However, thestructural integrity of the coupling element resists the radial force ofthe locking element, and the locking element is secured in the couplingelement thereby. This prevents the locking element from axially exitingthe coupling element.

[0024] In this manner, once the locking element is moved to the lockedposition, the screw, the coupling element, the locking element, and therod are all fixed relative to one another and to the bone. When all ofthe locking elements are so positioned, the implant is installed. Afterthe surgeon moves all of the locking elements in the orthopedic rodimplantation apparatus to the locked position, he closes the wounds ofthe patient and the surgery is complete.

[0025] Multiple screw and coupling element assemblies are generallynecessary to complete the full array of anchoring sites for a rodimmobilization system, however, the screw and coupling element assemblyof the invention is designed to be compatible with alternative rodsystems so that, where necessary, the invention may be employed torectify the failures of other systems, the implantation of which mayhave already begun.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a top view of a human vertebra.

[0027]FIG. 2 is a side view of a pair of adjacent vertebrae of the typeshown in FIG. 1.

[0028]FIG. 3 is a posterior view of a sequence of vertebrae of the typeshown in FIGS. 1 and 2.

[0029]FIGS. 4a, 4 b and 4 c are side, top, and cutaway side views of ascrew suitable for use in the invention.

[0030]FIGS. 4d and 4 e are side cutaway views of a screwdriving toolsuitable for driving the screw of FIGS. 4a, 4 b and 4 c.

[0031]FIGS. 5a, 5 b and 5 c are front, side and top views of a couplingelement suitable for use in the invention.

[0032]FIGS. 6a, 6 b, 6 c, 6 d and 6 e are front, side, front cutaway,side cutaway, and top views of a locking element suitable for use in theinvention.

[0033]FIG. 7 is a front cutaway view of the screw of FIGS. 4a-c, thecoupling element of FIGS. 5a-c, the locking element of FIGS. 6a-e, and arod, with the locking element in an unlocked position.

[0034]FIG. 8 is front view of the screw of FIGS. 4a-c, the couplingelement of FIGS. 5a-c, the locking element of FIGS. 6a-e, and a rod,with the locking element in a locked position.

[0035]FIG. 9 is a side cutaway view of the screw of FIGS. 4a-c, thecoupling element of FIGS. 5a-c, the locking element of FIGS. 6a-e, andthe screwdriving tool of FIGS. 4d-e.

[0036]FIGS. 10a and 10 b are front and side cutaway views of a wrenchingtool suitable for wrenching hexagonal protrusions of the locking elementof FIGS. 6a-e.

DETAILED DESCRIPTION OF THE INVENTION

[0037] While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of implantation are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of this invention.Accordingly, the descriptions which follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope.

[0038] In an embodiment, the invention provides a screw and couplingelement assembly for use with an orthopedic rod implantation apparatus.The assembly includes a securing element such as, for example, a screw,that has a head and a shaft that extends from the head. Other securingelements can include, for example, lamina hooks and sacral blocks.

[0039] Accordingly, FIG. 4a illustrates a side view of a screw 120suitable for use in the invention. The screw 120 includes a head 122 anda shaft 126 that extends from the head 122. The shaft 126 is shown ashaving a tapered shape with a high pitch thread 128. It shall beunderstood that a variety of shaft designs are interchangeable with thescrew of the invention. The specific choice of shaft features, such asthread pitch, shaft diameter to thread diameter ratio, and overall shaftshape, should be made be the physician with respect to the conditions ofthe individual patient's bone, however, the invention is compatible witha wide variety of shaft designs.

[0040] Preferably, the head has an engagement surface that can beengaged by a screwdriving tool. In this regard, one of the head and thetool can have a polygonal recess and the other of the head and the toolcan have an external structure that fits within the recess.

[0041] Accordingly, referring again to FIG. 4a and also to FIGS. 4b-4 e,the head 122 of the illustrated screw 120 includes a hexagonalengagement surface 130 that fits within a hexagonal recess 140 a of ascrewdriving tool 140. The surface 130 defines a receiving locus for theapplication of a torque for driving the screw 120 into a vertebral bone.Of course, the specific shape of the surface 130 may be chosen tocooperate with any suitable screwdriving tool. For example, the surface130 may include an engagement surface of another shape, or a recess suchas, for example, a slot for receiving a standard screwdriver, ahexagonally shaped hole for receiving an allen wrench, or a threadingfor a correspondingly threaded post. Preferably, the surface 130 isco-axial with the generally elongate axis of the screw 120 and, mostparticularly, the shaft 126. Having the axes of the surface 130 and theshaft 126 co-linear facilitates step of inserting the screw 120 into thebone.

[0042] Preferably, the head has a curvate proximal portion from whichthe shaft extends. The curvate proximal portion can be a semi-sphericalshape, exhibiting an external contour that is equidistant from a centerpoint of the head. When the head has an engagement surface that can beengaged by a screwdriving tool, it is preferable that the engagementsurface does not disrupt the functionality of the curvate proximalportion as described herein.

[0043] Accordingly, referring also to FIG. 4a again, the head 122 of theillustrated screw 120 includes a hemisphere 122 a as the curvateproximal portion. The use of the hemisphere 122 a in this embodimentfrees the hexagonal engagement surface 130 to effectively receive thehexagonal recess 140 a of the screwdriving tool 140.

[0044] Further, the head 122 of the illustrated screw 120 is connectedto the shaft 126 at a neck 124. The diameter of the head 122 is equal tothe largest diameter of the shaft 126, and the neck 124 tapers to exposethe operative portions of the curvate proximal portion 122 a of the head122. This configuration permits the screw 120 to swing through a varietyof angles before its position is fixed, as described below. It should benoted that in other embodiments, the diameter of the shaft 126 can beless than or greater than the diameter of the head 122, and the neck 124may be un-tapered or differently tapered.

[0045] In this embodiment, the screw and coupling element assemblyfurther includes a coupling element and a locking element. The couplingelement has a seat within which the head of the screw can be seated suchthat the shaft of the screw protrudes from the coupling element. Thelocking element can be mated with the coupling element and thereaftercan be selectively moved through a plurality of positions including anunlocked position and a locked position. When the locking element is inthe unlocked position, the locking element presents a rod-receivingchannel and the head of the screw is movable in the seat of the couplingelement, such that the shaft of the screw can be directed in a pluralityof angles relative to the coupling element. When the locking element isin the locked position, a rod disposed within the rod-receiving channelis fixed relative to the coupling element, and the head of the screw isimmovable in the seat of the coupling element, such that the shaft ofthe screw is fixed at an angle relative to the coupling element. Moreparticularly, when the locking element is in the locked position, thelocking element is compression locked within the coupling element, thehead of the screw is compression locked within the seat of the couplingelement, and the rod is compression locked within the rod-receivingchannel. At least one feature on the locking element can be used to movethe locking element through the positions when the locking element isdisposed within the coupling element. Preferably, the feature comprisesan engagement surface that can be engaged by a corresponding surface ofa tool, such that the tool can engage the engagement surface of thefeature and effectively move the locking element. Preferably, thecorresponding surface of the tool can engage the engagement surface ofthe feature despite the presence of the rod in the rod-receivingchannel.

[0046] Accordingly, FIGS. 5a-c illustrate a coupling element 150suitable for use in the invention, in front, top, side, front cutaway,and side cutaway views, respectively. FIGS. 6a -e illustrate a lockingelement 185 suitable for use in the invention, in front, top, and sideviews, respectively. FIG. 7 illustrates a front cutaway view of thescrew 120 of FIG. 4, the coupling element 150, and the locking element185 disposed within the coupling element 150 in an unlocked position.FIG. 8 illustrates a front view of the screw 120 of FIG. 4, the couplingelement 150, and the locking element 185 disposed within the couplingelement 150 in a locked position. The coupling element 150 has asubstantially cylindrical inner surface 150 c that accepts a cylindricalouter surface 185 e of the locking element 185 for coaxial insertion androtational translation therein so the locking element 185 can be rotatedthrough a plurality of positions. At one extreme of the positionalspectrum enjoyed by this locking element 185 is the unlocked positionshown in FIG. 7. At the other extreme is the locked position shown inFIG. 8. In order to permit the locking element 185 to be moved throughthe positions, the locking element 185 has a feature on each end of thelocking element 185, having a surface defined by a hexagonal protrusion185 d extending beyond a respective end of the coupling element 150. Thehexagonal protrusions 185 d can each be engaged by a correspondingsurface of a tool such as, for example, the corresponding hexagonalrecess 142 a of the wrenching tool 142 shown in FIGS. 10a and 10 b. Sothat the hexagonal recess 142 a can engage the hexagonal protrusions 185d despite the presence of a rod 195 in a rod-receiving channel 190, thewrenching tool 142 has a slot 142 b that accommodates the rod 195 as thewrenching tool 142 is rotated to rotate the locking element 185.

[0047] Preferably, the seat of the coupling element can be defined by abore in the coupling element and a socket defined by a curvate volumeadjacent the bore. The curvate volume corresponds to the curvateproximal portion of the head of the screw such that the curvate proximalportion can be nested in the socket. When the curvate proximal portionof the head of the screw is nested in the socket, the shaft of the screwprotrudes from the bore, the curvate proximal portion cannot pass fullythrough the bore. When the locking element is in the unlocked position,the curvate proximal portion of the head of the screw can rotate andangulate in the socket such that the shaft of the screw can be directedthrough a range of angles relative to the coupling element. When thelocking element is in the locked position, the curvate proximal portionof the head of the screw is immovable in the socket such that the shaftof the screw is fixed at an angle relative to the coupling element.

[0048] Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, a seat 150 aof the illustrated coupling element 150 is defined by a bore 150 b inthe coupling element 150 and a socket defined by a curvate volume 150 cadjacent the bore 150 b. The curvate volume 150 c corresponds to thecurvate proximal portion 122 a of the head 122 such that the curvateproximal portion 122 a can be nested in the socket 150 c. It isunderstood that the head 122 of the screw 120 is held within the curvatevolume 150 c by the relative size of the curvate proximal portion 122 aas compared with the bore 150 b. More specifically, the bore 150 b has adiameter less than the diameter of the curvate proximal portion 122 a.When the curvate proximal portion 122 a is nested in the socket 150 c,the shaft 126 protrudes from the bore 150 a and the curvate proximalportion 122 a cannot pass fully through the bore 150 a. Further when thecurvate proximal portion 122 a is nested in the socket 150 c, and whenthe locking element 185 is in the unlocked position, the curvateproximal portion 122 a can rotate and angulate in the socket 150 c suchthat the shaft 126 can be directed through a range of angles relative tothe coupling element 150. Further when the curvate proximal portion 122a is nested in the socket 150 c, and when the locking element 185 is inthe locked position, the curvate proximal portion 122 a is immovable inthe socket 150 c such that the shaft 126 is fixed at an angle relativeto the coupling element 150.

[0049] Preferably, the locking and unlocking action of the lockingelement is effected as follows. The head of the screw has a distalportion defined by a compression surface and the locking element has apermissive surface that is presented to the compression surface of thehead of the screw when the locking element is in the unlocked position.When presented with the permissive surface of the locking element, thecompression surface of the head of the screw is unhindered such that thehead of the screw is movable in the seat of the coupling element. Thelocking element also has a confrontational surface that is presented tothe compression surface of the head of the screw when the lockingelement is in the locked position. The confrontational surface of thelocking element is defined by a recess that has a recessed surfacecorresponding to the compression surface of the head of the screw.Therefore, when the locking element is in the locked position: (1) thelocking element is compressed within the coupling element, (2) thecompression surface of the head of the screw is compressed by theconfrontational surface of the locking element such that the curvateproximal portion of the head of the screw is compressed toward the boreof the coupling element and the head of the screw is immovable in theseat of the coupling element, and (3) the compression surface of thehead of the screw seats in the recess of the confrontational surface andthereby is biased against retreat from the recess. The compressionsurface of the head of the screw can be a curvate surface and theconfrontational surface of the locking element can extend from an edgeof the permissive surface of the locking element and terminate in therecess of the confrontational surface. The confrontational surface ofthe locking element preferably becomes increasing confrontational andtherefore is gradually presented to the compression surface of the headof the screw as the locking element is moved from the unlocked positionto the locked position.

[0050] Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, theillustrated head 122 has a distal portion defined by a compressionsurface 122 b and the illustrated locking element 185 has a permissivesurface 185 a that is presented to the compression surface 122 b whenthe locking element 185 is in the unlocked position. When presented withthe permissive surface 185 a, the compression surface 122 b isunhindered such that the head 122 is movable in the seat 150 a. Further,the illustrated locking element 185 has a confrontational surface 185 bthat is presented to the compression surface 122 b when the lockingelement 185 is in the locked position. The confrontational surface 185 bis defined by a recess 185 c that has a recessed surface correspondingto the compression surface 122 b. When the illustrated locking element185 is in the locked position, (1) the locking element 185 is compressedwithin the coupling element 150, (2) the compression surface 122 a iscompressed by the confrontational surface 185 b such that the curvateproximal portion 122 a of the head 122 is compressed toward the bore 150b and the head 122 is immovable in the seat 150 a, and (3) thecompression surface 122 b seats in the recess 185 c and thereby isbiased against retreat from the recess 185 c. The illustratedcompression surface 122 a is a curvate surface and the confrontationalsurface 185 b extends from an edge of the permissive surface 185 a andterminates in the recess 185 c. The confrontational surface 185 b istapered to become increasing confrontational as the locking element 185is moved from the unlocked position to the locked position and thereforeis gradually presented to the compression surface 122 a as the lockingelement 185 is moved from the unlocked position to the locked position.

[0051] Preferably, the rod-receiving channel, presented by the lockingelement when the locking element is in the unlocked position, is definedby substantially parallel walls. When the locking element is in thelocked position, the walls are compressed toward one another such thatthe rod is compressed within the channel and thereby fixed relative tothe coupling element. Preferably, the walls are increasingly compressedtoward one another as the locking element is moved from the unlockedposition to the locked position.

[0052] Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, therod-receiving channel 190 that is presented by locking element 185 whenthe locking element 185 is in the unlocked position has substantiallyparallel walls 190 a, 190 b. As the locking element 185 is moved fromthe unlocked position to the locked position, the walls 190 a, 190 b areincreasingly compressed toward one another. When the locking element 185is in the locked position, the walls 190 a, 190 b are compressed towardone another such that the rod 195 is compressed within the channel 190and thereby fixed relative to the coupling element 150.

[0053] Preferably, the coupling element has a bore that permits use ofthe screwdriving tool when the head is seated in the seat, allowing thescrewdriving tool to engage the head as described above. Alsopreferably, the locking element has a bore that permits use of thescrewdriving tool when the locking element is disposed within thecoupling element in an unlocked position and the head is seated in theseat, allowing the screwdriving tool to engage the head as describedabove.

[0054] Accordingly, with reference also to FIGS. 5a-c, 6 a-e, 7 and 8,FIG. 9 illustrates a side cutaway view of the screw 120, couplingelement 150, locking element 185, and screwdriving tool 140. It can beseen that a top surface of the coupling element 150 has a bore 197through which the screwdriving tool 140, which is used to insert thescrew 120 into the bone, may access and rotate the screw 120 through thecoupling element 150. It can also be seen that a top surface of thelocking element 150 has a bore 199 through which the screwdriving tool140 may access and rotate the screw 120 through the locking element 185when the locking element 185 is in the unlocked position.

[0055] Referring now to FIGS. 5a-c, 6 a-e, 7-9 and 10 a-10 b, thepreferred method of implantation and assembly is described hereinbelow.First, the locking element 185 is disposed within the coupling element150 so that it can be selectively moved. This can be accomplished bycoaxially inserting the locking element 185 into the coupling element150, contacting the cylindrical outer surface of the locking element 185with the substantially cylindrical inner surface 150 c of the couplingelement 150.

[0056] Once the locking element 185 is disposed within the couplingelement 150 in this manner, the wrenching tool 142 shown in FIGS. 10a-10b can be used to engage the hexagonal protrusions 185 d of the lockingelement 185 and rotate the locking element 195 within the couplingelement 150 until the locking element 185 is in the unlocked position asshown in FIG. 7.

[0057] When the locking element 185 is in the unlocked position, thebore 199 of the locking element and the bore 197 of the coupling elementpermit the insertion of the screw 120 into the seat 150 a. Moreparticularly, the surgeon can pass the shaft 126 of the screw 120 andthe head 122 of the screw through the bores 199 and 197, but only theshaft 126 will pass through the bore 150 b of the coupling element 150.As stated above, the curvate proximal portion 122 a of the head 122 willnot pass through the bore 150 b, but instead will nest in the seat 150 ain the curvate volume 150 c of the coupling element 150. The surgeon isthen able to freely rotate and angulate the screw 120 in the socket 150c to direct the shaft 126 in the clinically appropriate direction forsecure lodging in a vertebral bone.

[0058] It should be noted that while the insertion of the lockingelement 185 into the coupling element 150 and the subsequent insertionof the screw 120 through the bores 199 and 197 has been described, it ispossible to pre-assemble these elements in this configuration prior todelivery to the surgeon to minimize the effort and time required fromthe surgeon in preparing the elements for operative use.

[0059] Once the surgeon directs the shaft 126 of the screw 120 in theclinically appropriate direction, he is able to pass the operative endof the screwdriving tool 140 shown in FIGS. 4d and 4 e through the bore199 and the bore 197 to engage the hexagonal engagement surface 130 ofthe head 122 of the screw 120. As stated above, the operative end of thescrewdriving tool 140 has a hexagonal recess 140 a for engaging thehexagonal engagement surface 130 and rotating the screw 120 to drive theshaft 126 of the screw 120 into the vertebral bone. A pre-drill hole isusually provided in the bone, into which it is desired that the screw120 be disposed. The hole may be pre-tapped, or the external threading128 of the screw 120 may include a self-tapping edge.

[0060] Typically, the surgeon will repeat the process described aboveusing additional screws, coupling elements, and locking elements,lodging the additional screws into the same vertebral bone or othervertebral bones, depending on the clinically desirable result. To thatend, the invention encompasses an orthopedic rod implantation apparatushaving a plurality of screws and coupling elements of the typesdescribed above, and at least one elongate rod. Many implantations willrequire the use of two rods, however, only one rod or more than two rodsmay be necessary. The surgeon will, for example, lodge two screws into afirst verterbal bone (the screws are positioned laterally adjacent oneanother in the same bone, one in each pedicle), and lodge two otherscrews into a second vertebral bone (the screws are positioned laterallyadjacent one another in the same bone, one in each pedicle) that may beadjacent the first vertebral bone or may be separated from the firstvertebral bone by other vertebral bones that are damaged or unstable.

[0061] In a healthy spine, each screw in one of the pairs would roughlyalign with the corresponding screw in the other pair, because thevertebral bones would be vertically aligned. However, in some cases, thescrews will not be aligned because the spine is laterally crooked andthe surgeon is installing the implant to realign the vertebral bones.Therefore, in such cases, once the screws are in place, and theassociated coupling elements and locking elements are in the unlockedposition, presenting respective rod-receiving channels, and free torotate and angulate with respect to the head of their associated screw,the surgeon inserts a rod into one rod-receiving channel, and thereafterinto another rod-receiving channel, so that the rod lines up theverterbral bones affected thereby in a clinically desirable manner,urging them, typically, into vertical alignment. The surgeon similarlyinserts a second rod into the remaining two rod receiving channels tobalance the alignment forces.

[0062] Once the rods are in the rod receiving channels, the surgeonproceeds to move each locking element 185 into the locked position shownin FIG. 8. The surgeon uses the wrenching tool 142 shown in FIGS. 10aand 10 b, engaging the hexagonal recess 142 a of the wrenching tool 142with one of the hexagonal protrusions 185 d of the locking element andmoving the wrenching tool 142 to rotate the hexagonal protrusion 185 dand thereby rotate the locking element 185. As the locking element 185is moved to the locked position, the permissive surface 185 a, of thelocking element 185, that is presented to the compression surface 122 bof the head 122 when the locking element 185 is in the unlockedposition, is removed and the compression surface 122 b is increasinglypresented with the confrontational surface 185 b. This causes thecurvate proximal portion 122 a of the head 122 to be increasinglycompressed toward the bore 150 b until the head 122 is immovable in theseat 150 a. Ultimately, the compression surface 122 b seats in therecess 185 c and thereby is biased against retreat from the recess 185.This prevents accidental reverse rotational slippage of the lockingelement 185 from occurring and moving the locking element to theunlocked position. The locking element 185 can still be moved back tothe unlocked position if the surgeon desires to correct an error or toreadjust the components, if the surgeon uses the wrenching tool 142 andapplies enough force to overcome the force that seats the compressionsurface 122 b in the recess 185 c.

[0063] In addition, as the locking element 185 is moved to the lockedposition, the rod-receiving channel 190, presented by the lockingelement 185 when the locking element 185 is in the unlocked position,gradually closes. Ultimately, the channel 190 is completely closed. Thisprevents the rod 195 from laterally exiting the locking element 185.Further, the walls 190 a and 190 b of the channel 190 are graduallycompressed toward one another, until they ultimately secure the rod 195between them so that the rod 195 is fixed relative to the couplingelement 150. This prevents the rod 195 from axially exiting the lockingelement 185.

[0064] In addition, as the locking element 185 is moved to the lockedposition, the locking element 185 itself is gradually compressed withinthe coupling element 150 until it ultimately is secured within thecoupling element 150. More specifically, as the rod 195 seeks toradially force the walls 190 a and 190 b apart, the outer surface of thelocking element 185 seeks to radially push against the inner surface 150c of the coupling element 150. However, the structural integrity of thecoupling element 150 resists the radial force of the locking element185, and the locking element 185 is secured in the coupling element 150thereby. This prevents the locking element 185 from axially exiting thecoupling element 150.

[0065] In this manner, once the locking element 185 is moved to thelocked position, the screw 120, the coupling element 150, the lockingelement 185, and the rod 195 are all fixed relative to one another andto the bone. When all of the locking elements 185 are so positioned, theimplant is installed. After the surgeon moves all of the lockingelements in the orthopedic rod implantation apparatus to the lockedposition, he closes the wounds of the patient and the surgery iscomplete.

[0066] While there has been described and illustrated embodiments of ascrew and coupling element assembly, for use with an orthopedic rodimplantation apparatus, it will be apparent to those skilled in the artthat variations and modifications are possible without deviating fromthe broad spirit and principle of the invention. The invention shall,therefore, be limited solely by the scope of the claims appended hereto.

What is claimed is:
 1. A screw and coupling element assembly for usewith an orthopedic rod implantation apparatus, comprising: a screw thathas a head and a shaft that extends from the head; a coupling elementthat has a seat within which the head can be seated such that the shaftprotrudes from the coupling element; and a locking element that can bemated with the coupling element and that thereafter can be selectivelymoved through a plurality of positions including an unlocked positionand a locked position; wherein when the locking element is in theunlocked position, the locking element presents a rod-receiving channel,and the head is movable in the seat such that the shaft can be directedin a plurality of angles relative to the coupling element; and whereinwhen the locking element is in the locked position, a rod disposedwithin the rod-receiving channel is fixed relative to the couplingelement, and the head is immovable in the seat such that the shaft isfixed at an angle relative to the coupling element; and wherein the headhas a distal portion defined by a compression surface, the lockingelement has a permissive surface that is presented to the compressionsurface when the locking element is in the unlocked position, and whenpresented with the permissive surface, the compression surface isunhindered such that the head is movable in the seat; and wherein thelocking element has a confrontational surface that is presented to thecompression surface when the locking element is in the locked position,and the confrontational surface is defined by a recess that has arecessed surface corresponding to the compression surface; and whereinwhen the locking element is in the locked position, the locking elementis compressed within the coupling element, the compression surface iscompressed by the confrontational surface such that the curvate proximalportion is compressed toward the bore and the head is immovable in theseat, and the compression surface seats in the recess and thereby isbiased against retreat from the recess.
 2. The assembly of claim 1,wherein the head has an engagement surface that can be engaged by ascrewdriving tool, and at least one of the elements has a bore thatpermits use of the tool when the head is seated in the seat.
 3. Theassembly of claim 2, wherein one of the head and the tool has apolygonal recess, and the other of the head and the tool has an externalstructure that fits within the recess.
 4. The assembly of claim 1,wherein the head has a curvate proximal portion from which the shaftextends, the seat is defined by a bore in the coupling element and asocket defined by a curvate volume adjacent the bore, the curvate volumecorresponds to the curvate proximal portion such that the curvateproximal portion can be nested in the socket, and when the curvateproximal portion is nested in the socket, the shaft protrudes from thebore, the curvate proximal portion cannot pass fully through the bore,when the locking element is in the unlocked position the curvateproximal portion can rotate and angulate in the socket such that theshaft can be directed through a range of angles relative to the couplingelement, and when the locking element is in the locked position thecurvate proximal portion is immovable in the socket such that the shaftis fixed at an angle relative to the coupling element.
 5. The assemblyof claim 1, wherein the compression surface is a curvate surface, theconfrontational surface extends from an edge of the permissive surfaceand terminates in the recess, and the confrontational surface isgradually presented to the compression surface as the locking element ismoved from the unlocked position to the locked position.
 6. The assemblyof claim 1, wherein the rod-receiving channel is defined bysubstantially parallel walls, and when the locking element is in thelocked position the walls are compressed toward one another such thatthe rod is compressed within the channel and thereby fixed relative tothe coupling element.
 7. An orthopedic rod implantation apparatus havingscrews and coupling elements, comprising: at least one elongate rod; anda plurality of screw and coupling element assemblies; wherein at leastone of the assemblies comprises a screw that has a head and a shaft thatextends from the head, a coupling element that has a seat within whichthe head can be seated such that the shaft protrudes from the couplingelement, and a locking element that can be mated with the couplingelement and that thereafter can be selectively moved through a pluralityof positions including an unlocked position and a locked position; andwherein when the locking element is in the unlocked position, thelocking element presents a rod-receiving channel, and the head ismovable in the seat such that the shaft can be directed in a pluralityof angles relative to the coupling element; and wherein when the lockingelement is in the locked position, the rod, if disposed within therod-receiving channel, is fixed relative to the coupling element, andthe head is immovable in the seat such that the shaft is fixed at anangle relative to the coupling element; and wherein the head has adistal portion defined by a compression surface, the locking element hasa permissive surface that is presented to the compression surface whenthe locking element is in the unlocked position, and when presented withthe permissive surface, the compression surface is unhindered such thatthe head is movable in the seat; and wherein the locking element has aconfrontational surface that is presented to the compression surfacewhen the locking element is in the locked position, and theconfrontational surface is defined by a recess that has a recessedsurface corresponding to the compression surface; and wherein when thelocking element is in the locked position, the locking element iscompressed within the coupling element, the compression surface iscompressed by the confrontational surface such that the curvate proximalportion is compressed toward the bore and the head is immovable in theseat, and the compression surface seats in the recess and thereby isbiased against retreat from the recess.
 8. The apparatus of claim 7,wherein the head has an engagement surface that can be engaged by ascrewdriving tool, and at least one of the coupling element and thelocking element has a bore that permits use of the tool when the head isseated in the seat.
 9. The apparatus of claim 8, wherein one of the headand the tool has a polygonal recess, and the other of the head and toolhas an external structure that fits within the recess.
 10. The apparatusof claim 7, wherein the head has a curvate proximal portion from whichthe shaft extends, the seat is defined by a bore in the coupling elementand a socket defined by a curvate volume adjacent the bore, the curvatevolume corresponds to the curvate proximal portion such that the curvateproximal portion can be nested in the socket, and when the curvateproximal portion is nested in the socket, the shaft protrudes from thebore, the curvate proximal portion cannot pass fully through the bore,when the locking element is in the unlocked position the curvateproximal portion can rotate and angulate in the socket such that theshaft can be directed through a range of angles relative to the couplingelement, and when the locking element is in the locked position thecurvate proximal portion is immovable in the socket such that the shaftis fixed at an angle relative to the coupling element.
 11. The apparatusof claim 7, wherein the compression surface is a curvate surface, theconfrontational surface extends from an edge of the permissive surfaceand terminates in the recess, and the confrontational surface isgradually presented to the compression surface as the locking element ismoved from the unlocked position to the locked position.
 12. Theapparatus of claim 7, wherein the rod-receiving channel is defined bysubstantially parallel walls, and when the locking element is in thelocked position the walls are compressed toward one another such thatthe rod is compressed within the channel and thereby fixed relative tothe coupling element.
 13. A locking assembly, comprising: a securingelement that has a head and a shaft that extends from the head; acoupling element that has a seat within which the head can be seatedsuch that the shaft protrudes from the coupling element; and a lockingelement that can be mated with the coupling element and that thereaftercan be selectively moved through a plurality of positions including anunlocked position and a locked position; wherein when the lockingelement is in the unlocked position, the locking element presents achannel for receiving a rod, and the head is movable in the seat suchthat the shaft can be directed in a plurality of angles relative to thecoupling element; and wherein when the locking element is in the lockedposition, the rod, if disposed within the channel, is fixed relative tothe coupling element, the head is immovable in the seat such that shaftis fixed at an angle relative to the coupling element, the lockingelement is compression locked within the coupling element, the head iscompression locked within the seat, and the rod, if disposed within thechannel, is compression locked within the channel.
 14. The assembly ofclaim 13, wherein: the seat is defined by a bore in the coupling elementand a socket adjacent the bore; the head can be nested in the socketsuch that head cannot pass fully through the bore but the shaftprotrudes from the bore; the locking element has an increasinglyconfrontational surface terminating in a recess that has a recessedsurface; the head has a compression surface corresponding to therecessed surface; and the channel is defined by walls of the lockingelement; wherein: when the locking element is moved from the unlockedposition to the locked position: the locking element is compressedwithin the coupling element; the walls are compressed toward one anothersuch that the rod, if disposed within the channel, is compressed withinthe channel and thereby fixed relative to the coupling element; thecompression surface is compressed by the confrontational surface suchthat the head is compressed toward the bore and rendered immovable inthe socket; and the compression surface seats in the recess and therebyis biased against retreat from the recess.
 15. The assembly of claim 13,wherein the locking element is moved through the plurality of positionsby rotating the locking element within the coupling element.
 16. Theassembly of claim 13, wherein the locking element is provided with atleast one engagement surface that can be engaged by a tool to move thelocking element through the plurality of positions.
 17. The assembly ofclaim 16, wherein the tool has a corresponding surface that engages theengagement surface and the tool accommodates the rod as the tool is usedto move the locking element through the plurality of positions.